In wireless communications an allowable set of carrier amplitudes, power levels, or ratios of power levels may be assigned, or “granted” to a transmitter. These values may be dynamic—the grant may change with time as communication conditions change.
High-Speed Packet Access (HSPA) is a collection of mobile telephony protocols that extend and improve the performance of existing mobile telephony protocols. Evolution of HSPA to support higher system throughput and performance has lead to the introduction of 16QAM modulation on the uplink. One of the items required to support Higher Order Modulation (HOM) is an enhanced pilot.
Several options have been disclosed to provide the enhanced pilot including boosting the power of the Dedicated Physical Control Channel (DPCCH), boosting the power of the Enhanced Dedicated Physical Control Channel (E-DPCCH) and introduction of a second DPCCH. In the case of boosting the power of the DPCCH, scheduling issues occur when the Enhanced Absolute Grant Channel (E-AGCH) needs to jump abruptly and the operating point is near the boundary of the power grant for BPSK and 16QAM modulation. If the power of the E-DPCCH is boosted or a second DPCCH is added, the range of the power ratio may need to be extended. An increase in the power ratio will require either the E-AGCH to have more bits to cover the higher range, or the step sizes must be increased in the E-AGCH absolute grant value.
Current solutions have system drawbacks and require careful consideration of side effects of implementation. Promising options appear to be to boost E-DPCCH power or add a second DPCCH since this will require changing the E-AGCH absolute grant value mapping table and should have minimal impact on the system.
An improved E-AGCH absolute grant value mapping table currently existing has some problems regarding how the table should be updated. One solution would be to add additional indices to support higher power ratio range required for 16QAM. This change requires adding bits to the E-AGCH to cover the additional index values. The additional bits require a format change as well as coding changes. Thus, adding bits has significant effect on the overall system configuration.
One solution is to keep the E-AGCH format as is, including the number of bits, the coding and the format. It is also desirable to retain the current structure of the mapping table.